On 2/7/23 16:29, Michael Walle wrote:
Honestly, not really? Some good number of SoCs will start the
watchdog
in ROM and these are also the ones that don't allow you to turn it
off.
I hope not, that sounds really risky. How would you debug such a
platform?
_Every single_ custom piece of industrial (as opposed to
consumer-grade)
hardware I've worked on as a consultant has had an external,
always-running, gpio-petted watchdog. It's simply just something that
the hardware designers include, and in some cases that's even due to
certification requirements. So an always-running, cannot-be-turned-off,
watchdog is a real thing, in real hardware, and if specs don't account
for that, well, the spec is just paper, and we can ignore it.
I agree. But on the other hand, you cannot assume or force the OS to
have a watchdog driver in the general case - which is as I understand
it - one goal of EFI.
Obviously, there are watchdogs that can be disabled and some which
cannot. I don't want to argue about the advantages and disadvantages.
For watchdogs which cannot be turned off, we can't really do anything
anyway after the handoff to the OS - except increasing its timeout if
thats possible.
For watchdogs that can be disabled (and are enabled in u-boot of
course),
there seems to be two use-cases:
(1) embedded EFI boot, that is you know exactly what you are
booting, i.e.
self compiled kernel with a watchdog driver
(2) booting a general OS via EFI, think of a debian boot CD for
example.
I agree, that for (1) the watchdog shouldn't be disabled. For (2) you
cannot assume the booting OS has a driver for the watchdog, let it be an
older version of a distribution which just haven't the SoC watchdog
driver
enabled or maybe because there is no driver for it at all (yet).
Is there a way, to have the watchdog disabled for case (2) while also
having the possibity to use bootm/booti/bootz and keep the watchdog
enabled? Basically I want the following:
(1) board boots with watchdog enabled
(2) u-boot services watchdog
(3a) booting embedded linux with booti (watchdog enabled) or
(3b) booting generic OS with bootefi (watchdog disabled)
The missing case is booting an embedded linux with bootefi, which
would be nice to have. But I don't really see it as a use-case for
our board.
-michael
For SUNXI boards disabling CONFIG_WATCHDOG_AUTOSTART solved the
problem with the very short maximum expiration time of the watchdog.
I can't follow you here. What "very short maximum expiration time"?
With CONFIG_WATCHDOG_AUTOSTART disabled, the watchdog won't be kicked
by u-boot, right? wdt->running will never be set to true and
wdt_cyclic() will be a noop.
-michael
The sunxi boards failed to boot with CONFIG_WATCHDOG_AUTOSTART because
16s is too short for Linux to install a watchdog driver. With
CONFIG_WATCHDOG_AUTOSTART=n the watchdog is not running and the boards boot.
Best regards
Heinrich
